We are continuing to study the role of prostaglandin in ovarian function. We are investigating two ovarian compartments. In the corpus luteum we have shown that in vivo, the administration of PGF 2 alpha to normal women in the luteal phase of the cycle will not alter corpus luteum function, whereas in vitro PGF2 will stimulate the progesterone production of the corpus luteum. This stimulation was shown to involve cyclic AMP. We have also shown that there is a marked difference between corpora lutea from cyclic and pregnant women in terms of steroidogenesis and cyclic AMP synthesis. In our studies on the follicle we have shown that both prostaglandins, E and F, increase markedly in rabbit Graafian follicles, prior to ovulation and that this increase can be inhibited with indomethacin. This increase in prostaglandin appears to be limited to those follicles that go on to ovulate. From these and previous data, we are proposing a hypothetical model for the mechanism of ovulation in the rabbit and are attempting to test this hypothesis in our animal model, as well as in primates.